Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.
Particulate matter sensors may correlate a measured change in electrical conductivity (or resistivity) between a pair of electrodes placed on a substrate surface of the sensor with the amount of particulate matter deposited between the electrodes. Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output.
Other attempts to address particulate matter sensor performance include guiding a portion of exhaust toward the particulate matter sensor. One example approach is shown by Liu et al. in U.S. Pat. No. 8,756,913. Therein, a pair of intersecting tubes are located along an exhaust passage with a sensor located in an upper portion of the exhaust passage fluidly coupled to an axial tube of the pair of tubes. The tubes are configured to receive exhaust gas from a variety of locations within the exhaust passage to increase an accuracy of data provided by the sensor.
However, the inventors herein have recognized potential issues with such systems. As one example, the pair of tubes may conduct large particulate matter and/or water droplets onto the sensor. This may decrease a reliability of data provided by the sensor with regards to PF degradation.
The inventors herein have recognized the above issues and identified an approach to at least partly address both the general issues as well as particular issues with Liu. In one example, the issues described above may be addressed by a system comprising two fully intersecting tubes fluidly coupled to an outer circular tube, and where the intersecting and circular tubes are fluidly coupled to a sensor via a bent tube (an L- or C-shaped tube, for example) in an upstream direction relative to exhaust flow. In this way, a likelihood of large particulates and water droplets flowing to the sensor is decreased.
As one example, the circular tube is radially spaced away from interior surfaces of an exhaust pipe. The intersecting tubes and the outer circular tube comprise inlets facing a direction of incoming exhaust flow. The inlets are configured to admit exhaust flow into a common interior passage of the circular and intersecting tubes. Exhaust gas in the interior space may flow into the L-shaped tube in an upstream direction opposite a direction of incoming exhaust flow. This may decrease and/or prevent large particulates and/or water droplets from flowing to a PM sensor located in an upper portion of the L-shaped tube due to a greater momentum of the large particulates and/or water droplets carrying them to a back wall of the interior space. Overall, functioning of the PM sensor may be improved and may be more reliable.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.